The present invention relates generally to the fabrication of optic fiber array blocks and more particularly to methods and apparatuses for hermetically sealing the same.
Recent innovations in the design and fabrication of optical switching systems have made possible switching systems having thousands of optic fiber inputs and outputs.
FIG. 1 represents, generally, an optical switching system in accordance with the prior art. System 100, shown in FIG. 1, includes a first optic fiber array block 110, a first lens array 120, a first mirror array 130, a second mirror array 140, a second lens array 150, and a second optic fiber array block 160. In practice the optic fiber arrays may be bonded to the lens arrays to form collimator arrays. The optic fiber array block 110 and 160 contain an array of optic fibers that transmit light beams. For example, a fiber of optic fiber array block 110 may transmit a beam to a lens of the first lens array 120. The first lens array 120 focuses the beam for transmission to the first mirror array 130. The mirror arrays contain an array of movable mirrors that are positioned to reflect and redirect beams from the individual fibers of the fiber arrays. The beam is redirected from the first mirror array 130 to the second mirror array 140. From the second mirror array 140, the beam is directed to a lens of the second lens array 150, focused, and transmitted to the appropriate individual fiber of the output optic fiber array block 160. The optical switching system 100 allows light beams from any fiber of the first optic fiber array 110 to be directed to any fiber of the second optic fiber array block 160. In this way, optical signals are switched from one fiber to another.
Fiber array blocks, such as fiber array block 10, are typically formed by inserting fibers into a plate having an array of holes formed within it. To facilitate inserting the fibers, two fiber array plates may be joined to form a fiber block. The first plate has an array of holes that are substantially greater than the fiber diameter for coarsely positioning the fibers and the other plate has holes that are only slightly larger than the fiber diameter for finely positioning the fibers.
In order for the optical switching system to function properly, the fibers must be held in position with the fiber array plate. For an optical switching system such as system 100 to be functional, the transmitted beams must meet certain criteria within specified tolerances. Movement of the fibers within the fiber array block may detrimentally affect the characteristics of the transmitted beam. Beam parallelism is the relative angle of different beams from the same fiber array or lens array. If the fibers are allowed to shift position it can cause the beams to be angled relative to one another. If the output beams from the fiber block are not parallel, they won""t shine directly through the corresponding lens of the lens array and consequently won""t shine directly on the corresponding mirror of the mirror array. If less of the beam impacts the mirror, then less of the beam is transmitted through the switching system. At some point this loss of signal strength renders the system inoperable.
Typically an epoxy is placed between the two fiber array plates that form the fiber array block. After the fibers are in place, liquid epoxy may be poured between the two plates. The epoxy then fills the gaps between the fibers and the holes of each plate. After curing, the epoxy becomes rigid and holds the fibers in place.
Although using epoxy to hold the fibers in place is straightforward and relatively inexpensive, the use of epoxy has several drawbacks. The epoxy is an organic material and may degrade significantly over time. The epoxy does not provide a hermetic seal to protect system components from the environment. In humid environments especially, the epoxy may allow the transmission of water vapor through the system. Water vapor may damage the surface of the mirrors and other components of the system.
Additionally, the mechanical strength of the epoxy may deteriorate over time, eventually allowing the fibers to shift.
A method for hermetically sealing a fiber array block is described. A fiber array plate is fabricated. The fiber array plate has an array of tapered holes formed therein. An adhering metal layer is deposited upon the fiber array plate. A preform is positioned on the fiber array plate so that the array of holes in the preform correspond to the array of holes in the array plate. Fibers having an adhering metal layer deposited thereon are then inserted through the fiber array plate. The fiber array plate is then heated such that the preform melts causing the material of the preform to fill any gaps between the fiber array plates and the fiber, thus forming a hermetic seal between the fiber array and the fiber.
Other features and advantages of the present invention will be apparent from the accompanying drawings, and from the detailed description, that follows below.